edited by Robert M. Hashway
Praeger, 1990
Buku Referensi
Stoff, Sheldon Ptaschevitch, author
Harper & Row , 1969
Buku Teks
Marland, Sidney P., author
McGraw-Hill, 1974
Buku Teks
Caravan, Jill, author
Todtri Production Limited, 1996
Buku Referensi
Department of Health, education and welfare, 1964
Buku Teks